Fin field-effect transistor and method of forming the same

ABSTRACT

A semiconductor device includes a semiconductor fin. The semiconductor device includes a metal gate disposed over the semiconductor fin. The semiconductor device includes a gate dielectric layer disposed between the semiconductor fin and the metal gate. The semiconductor device includes first spacers sandwiching the metal gate. The first spacers have a first top surface and the gate dielectric layer has a second top surface, and the first top surface and a first portion of the second top surface are coplanar with each other. The semiconductor device includes second spacers further sandwiching the first spacers. The second spacers have a third top surface above the first top surface and the second top surface. The semiconductor device includes a gate electrode disposed over the metal gate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority under 35 U.S. § 120as a continuation of U.S. Non-Provisional application Ser. No.17/688,364, filed on Mar. 7, 2022, titled “FIN FIELD-EFFECT TRANSISTORAND METHOD OF FORMING THE SAME,” which is related to and claims priorityunder 35 U.S. § 120 as a continuation of U.S. Non-Provisionalapplication Ser. No. 16/859,538, filed on Apr. 27, 2020, titled “FINFIELD-EFFECT TRANSISTOR AND METHOD OF FORMING THE SAME,” the entirecontents of both of which are incorporated herein by reference for allpurposes.

BACKGROUND

The present disclosure generally relates to semiconductor devices, andparticularly to methods of making a non-planar transistor.

The semiconductor industry has experienced rapid growth due tocontinuous improvements in the integration density of a variety ofelectronic components (e.g., transistors, diodes, resistors, capacitors,etc.). For the most part, this improvement in integration density hascome from repeated reductions in minimum feature size, which allows morecomponents to be integrated into a given area.

Fin Field-Effect Transistor (FinFET) devices are becoming commonly usedin integrated circuits. FinFET devices have a three-dimensionalstructure that comprises a fin protruding from a substrate. A gatestructure, configured to control the flow of charge carriers within aconductive channel of the FinFET device, wraps around the fin. Forexample, in a tri-gate FinFET device, the gate structure wraps aroundthree sides of the fin, thereby forming conductive channels on threesides of the fin.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a perspective view of a fin field-effect transistor(FinFET) device, in accordance with some embodiments.

FIG. 2 illustrates a flow chart of an example method for making anon-planar transistor device, in accordance with some embodiments.

FIGS. 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and20 illustrate cross-sectional views of an example FinFET device (or aportion of the example FinFET device) during various fabrication stages,made by the method of FIG. 2 , in accordance with some embodiments.

FIG. 21 illustrates a cross-sectional view of another example FinFETdevice, in accordance with some embodiments.

FIG. 22 illustrates a cross-sectional view of yet another example FinFETdevice, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The terms “about” and “substantially” can indicate a value of a givenquantity that varies within 5% of the value (e.g., ±1%, ±2%, ±3%, ±4%,±5% of the value).

Embodiments of the present disclosure are discussed in the context offorming a FinFET device, and in particular, in the context of forming areplacement gate of a FinFET device. In some embodiments, a dummy gatestructure is formed over a fin. A first gate spacer is formed around thedummy gate structure, and a second gate spacer is formed around thefirst gate spacer. After an interlayer dielectric (ILD) layer is formedaround the second gate spacer, the dummy gate structure is removed.Next, upper portions of the first gate spacer are removed while lowerportions of the first gate spacer remain. After removing the upperportions of the first gate spacer, a gate trench is formed in the ILDlayer. The gate trench has a lower trench between the lower portions ofthe first gate spacer and has an upper trench over the lower trench,where the upper trench may be wider than the lower trench. Next, a gatedielectric layer, one or more work function layers, an optional cappinglayer, and a glue layer are successively formed in the gate trench.Next, the glue layer is selectively removed from the upper trench by afirst wet etch process, the optional capping layer (if formed) isremoved from the upper trench by a second wet etch process, and the workfunction layer(s) are selectively removed from the upper trench by athird wet etch process. After the third wet etch process, the gatedielectric layer remains extending along the trench. Further, a portionof the gate dielectric layer, remaining portions of the work functionlayer(s), a remaining portion of the capping layer, and a remainingportion of the glue layer are disposed in the lower trench. Theremaining portions of the work function layer(s), the capping layer, andthe glue layer can present a concave upper surface that is below aninterface between the upper trench and the lower trench. Next, a gateelectrode is formed in the trench to be in contact with the concaveupper surface of the work function layer(s), the capping layer, and theglue layer. The gate electrode may overlay the portion of the gatedielectric layer in the lower trench, and the remaining portions of thework function layer(s), the capping layer, and the glue layer in thelower trench. Next, a fourth wet etch process is performed to remove thegate dielectric layer not overlaid by the gate electrode, whileremaining the gate electrode substantially intact. In some embodiments,the remaining portions of the work function layer(s), the capping layer,and the glue layer may be collectively referred to as a metal gate.

Metal gates over a fin formed by the above described method have a lagerdistance (e.g., pitch) in between, thereby reducing metal gate leakagein advanced processing nodes. The various selective etch processes usedin the above described method can precisely control the end point of theetching process, avoid attaching undesired metal material to the gatespacers during formation of the gate electrode, and avoid the loadingeffect during etch back of the various layers of the metal gates. As aresult, the gate height of the metal gate is precisely controlled. Inaddition, the critical dimension (CD) of the metal gate and the sidewallprofiles of the ILD layer and an overlying mask layer are preserved.

FIG. 1 illustrates a perspective view of an example FinFET device 100,in accordance with various embodiments. The FinFET device 100 includes asubstrate 102 and a fin 104 protruding above the substrate 102.Isolation regions 106 are formed on opposing sides of the fin 104, withthe fin 104 protruding above the isolation regions 106. A gatedielectric 108 is along sidewalls and over a top surface of the fin 104,and a gate 110 is over the gate dielectric 108. Source/drain regions112D and 112S are in the fin 104 and on opposing sides of the gatedielectric 108 and the gate 110. The source/drain regions 112D and 112Sextend outward from the gate 110. FIG. 1 is provided as a reference toillustrate a number of cross-sections in subsequent figures. Forexample, cross-section B-B extends along a longitudinal axis of the gate110 of the FinFET device 100. Cross-section A-A is perpendicular tocross-section B-B and is along a longitudinal axis of the fin 104 and ina direction of, for example, a current flow between the source/drainregions 112S/112D. Subsequent figures refer to these referencecross-sections for clarity.

FIG. 2 illustrates a flowchart of a method 200 to form a non-planartransistor device, according to one or more embodiments of the presentdisclosure. For example, at least some of the operations of the method200 can be used to form a FinFET device (e.g., FinFET device 100), anano-sheet transistor device, a nanowire transistor device, a verticaltransistor, or the like. It is noted that the method 200 is merely anexample, and is not intended to limit the present disclosure.Accordingly, it is understood that additional operations may be providedbefore, during, and after the method 200 of FIG. 2 , and that some otheroperations may only be briefly described herein. In some embodiments,operations of the method 200 may be associated with cross-sectionalviews of an example FinFET device at various fabrication stages as shownin FIGS. 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, and 19, respectively, which will be discussed in further detail below.

In brief overview, the method 200 starts with operation 202 of providinga substrate. The method 200 continues to operation 204 of forming a fin.The method 200 continues to operation 206 of forming isolation regions.The method 200 continues to operation 208 of forming dummy gatestructures. The dummy gate structures may straddle a central portion ofthe fin. The method 200 continues to operation 210 of forming lightlydoped drain (LDD) regions and gate spacers. The gate spacers areextended along sidewalls of the dummy gate structure. The method 200continues to operation 212 of growing source/drain regions. The method200 continues to operation 214 of forming an interlayer dielectric(ILD). The method 200 continues to operation 216 of removing the dummygate structure. Upon the dummy gate structure being removed, the centralportion of the fin is re-exposed. The method 200 continues to operation218 of depositing a gate dielectric layer, a work function layer, acapping layer, and a glue layer. The method 200 continues to operation220 of removing a portion of the glue layer. The method 200 continues tooperation 222 of removing a portion of the capping layer. The method 200continues to operation 224 of removing a portion of the work functionlayer. The method 200 continues to operation 226 of forming a metalstructure. Such a metal structure is sometimes referred to as a gateelectrode. The method 200 continues to operation 228 of removing aportion of the gate dielectric material. The method 200 continues tooperation 230 of depositing a dielectric material. The method 200continues to operation 232 of forming a gate contact.

As mentioned above, FIGS. 3-19 each illustrates, in a cross-sectionalview, a portion of a FinFET device 300 at various fabrication stages ofthe method 200 of FIG. 2 . The FinFET device 300 is substantiallysimilar to the FinFET device 100 shown in FIG. 1 , but with multiplegate structures. For example, FIGS. 3-6 illustrate cross-sectional viewsof the FinFET device 300 along cross-section B-B (as indicated in FIG. 1); and FIG. 7-19 illustrate cross-sectional views of the FinFET device300 along cross-section A-A (as indicated in FIG. 1 ). Although FIGS.3-19 illustrate the FinFET device 300, it is understood the FinFETdevice 300 may include a number of other devices such as inductors,fuses, capacitors, coils, etc., which are not shown in FIGS. 3-19 , forpurposes of clarity of illustration.

Corresponding to operation 202 of FIG. 2 , FIG. 3 is a cross-sectionalview of the FinFET device 300 including a semiconductor substrate 302 atone of the various stages of fabrication. The substrate 302 may be asemiconductor substrate, such as a bulk semiconductor, asemiconductor-on-insulator (SOI) substrate, or the like, which may bedoped (e.g., with a p-type or an n-type dopant) or undoped. Thesubstrate 302 may be a wafer, such as a silicon wafer. Generally, an SOIsubstrate includes a layer of a semiconductor material formed on aninsulator layer. The insulator layer may be, for example, a buried oxide(BOX) layer, a silicon oxide layer, or the like. The insulator layer isprovided on a substrate, typically a silicon or glass substrate. Othersubstrates, such as a multi-layered or gradient substrate may also beused. In some embodiments, the semiconductor material of the substrate302 may include silicon; germanium; a compound semiconductor includingsilicon carbide, gallium arsenic, gallium phosphide, indium phosphide,indium arsenide, and/or indium antimonide; an alloy semiconductorincluding SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; orcombinations thereof.

Corresponding to operation 204 of FIG. 2 , FIG. 4 is a cross-sectionalview of the FinFET device 300 including a (semiconductor) fin 404 at oneof the various stages of fabrication. Although one fin is shown in theillustrated embodiment of FIG. 4 (and the following figures), it shouldbe appreciated that the FinFET device 300 can include any number of finswhile remaining within the scope of the present disclosure. In someembodiments, the fin 404 is formed by patterning the substrate 302using, for example, photolithography and etching techniques. Forexample, a mask layer, such as a pad oxide layer 406 and an overlyingpad nitride layer 408, is formed over the substrate 302. The pad oxidelayer 406 may be a thin film comprising silicon oxide formed, forexample, using a thermal oxidation process. The pad oxide layer 406 mayact as an adhesion layer between the substrate 302 and the overlying padnitride layer 408. In some embodiments, the pad nitride layer 408 isformed of silicon nitride, silicon oxynitride, silicon carbonitride, thelike, or combinations thereof. The pad nitride layer 408 may be formedusing low-pressure chemical vapor deposition (LPCVD) or plasma enhancedchemical vapor deposition (PECVD), for example.

The mask layer may be patterned using photolithography techniques.Generally, photolithography techniques utilize a photoresist material(not shown) that is deposited, irradiated (exposed), and developed toremove a portion of the photoresist material. The remaining photoresistmaterial protects the underlying material, such as the mask layer inthis example, from subsequent processing steps, such as etching. Forexample, the photoresist material is used to pattern the pad oxide layer406 and pad nitride layer 408 to form a patterned mask 410, asillustrated in FIG. 4 .

The patterned mask 410 is subsequently used to pattern exposed portionsof the substrate 302 to form trenches (or openings) 411, therebydefining a fin 404 between adjacent trenches 411 as illustrated in FIG.4 . When multiple fins are formed, such a trench may be disposed betweenany adjacent ones of the fins. In some embodiments, the fin 404 isformed by etching trenches in the substrate 302 using, for example,reactive ion etch (RIE), neutral beam etch (NBE), the like, orcombinations thereof. The etching may be anisotropic. In someembodiments, the trenches 411 may be strips (viewed from the top)parallel to each other, and closely spaced with respect to each other.In some embodiments, the trenches 411 may be continuous and surround thefin 404. The fin 404 may also be referred to as fin 404 hereinafter.

The fin 404 may be patterned by any suitable method. For example, thefin 404 may be patterned using one or more photolithography processes,including double-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers, or mandrels, may then be usedto pattern the fin.

Corresponding to operation 206 of FIG. 2 , FIG. 5 is a cross-sectionalview of the FinFET device 300 including isolation regions 500 at one ofthe various stages of fabrication. The isolation regions 500, which areformed of an insulation material, can electrically isolate neighboringfins from each other. The insulation material may be an oxide, such assilicon oxide, a nitride, the like, or combinations thereof, and may beformed by a high density plasma chemical vapor deposition (HDP-CVD), aflowable CVD (FCVD) (e.g., a CVD-based material deposition in a remoteplasma system and post curing to make it convert to another material,such as an oxide), the like, or combinations thereof. Other insulationmaterials and/or other formation processes may be used. In theillustrated embodiment, the insulation material is silicon oxide formedby a FCVD process. An anneal process may be performed once theinsulation material is formed. A planarization process, such as achemical mechanical polish (CMP), may remove any excess insulationmaterial and form top surfaces of the isolation regions 500 and a topsurface of the fin 404 that are coplanar (not shown, the isolationregions 500 will be recessed as shown in FIG. 5 ). The patterned mask410 (FIG. 4 ) may also be removed by the planarization process.

In some embodiments, the isolation regions 500 include a liner, e.g., aliner oxide (not shown), at the interface between each of the isolationregions 500 and the substrate 302 (fin 404). In some embodiments, theliner oxide is formed to reduce crystalline defects at the interfacebetween the substrate 302 and the isolation region 500. Similarly, theliner oxide may also be used to reduce crystalline defects at theinterface between the fin 404 and the isolation region 500. The lineroxide (e.g., silicon oxide) may be a thermal oxide formed through athermal oxidation of a surface layer of the substrate 302, althoughother suitable method may also be used to form the liner oxide.

Next, the isolation regions 500 are recessed to form shallow trenchisolation (STI) regions 500, as shown in FIG. 5 . The isolation regions500 are recessed such that the upper portions of the fin 404 protrudefrom between neighboring STI regions 500. Respective top surfaces of theSTI regions 500 may have a flat surface (as illustrated), a convexsurface, a concave surface (such as dishing), or combinations thereof.The top surfaces of the STI regions 500 may be formed flat, convex,and/or concave by an appropriate etch. The isolation regions 500 may berecessed using an acceptable etching process, such as one that isselective to the material of the isolation regions 500. For example, adry etch or a wet etch using dilute hydrofluoric (DHF) acid may beperformed to recess the isolation regions 500.

FIGS. 3 through 5 illustrate an embodiment of forming one or more fins(such as fin 404), but a fin may be formed in various differentprocesses. For example, a top portion of the substrate 302 may bereplaced by a suitable material, such as an epitaxial material suitablefor an intended type (e.g., N-type or P-type) of semiconductor devicesto be formed. Thereafter, the substrate 302, with epitaxial material ontop, is patterned to form the fin 404 that includes the epitaxialmaterial.

As another example, a dielectric layer can be formed over a top surfaceof a substrate; trenches can be etched through the dielectric layer;homoepitaxial structures can be epitaxially grown in the trenches; andthe dielectric layer can be recessed such that the homoepitaxialstructures protrude from the dielectric layer to form one or more fins.

In yet another example, a dielectric layer can be formed over a topsurface of a substrate; trenches can be etched through the dielectriclayer; heteroepitaxial structures can be epitaxially grown in thetrenches using a material different from the substrate; and thedielectric layer can be recessed such that the heteroepitaxialstructures protrude from the dielectric layer to form one or more fins.

In embodiments where epitaxial material(s) or epitaxial structures(e.g., the heteroepitaxial structures or the homoepitaxial structures)are grown, the grown material(s) or structures may be in situ dopedduring growth, which may obviate prior and subsequent implantationsalthough in situ and implantation doping may be used together. Stillfurther, it may be advantageous to epitaxially grow a material in anNMOS region different from the material in a PMOS region. In variousembodiments, the fin 404 may include silicon germanium (Si_(x)Ge_(1-x),where x can be between 0 and 1), silicon carbide, pure or substantiallypure germanium, a III-V compound semiconductor, a II-VI compoundsemiconductor, or the like. For example, the available materials forforming III-V compound semiconductor include, but are not limited to,InAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, andthe like.

Corresponding to operation 208 of FIG. 2 , FIG. 6 is a cross-sectionalview of the FinFET device 300 including a dummy gate structure 600 atone of the various stages of fabrication. The dummy gate structure 600includes a dummy gate dielectric 602 and a dummy gate 604, in someembodiments. A mask 606 may be formed over the dummy gate structure 600.To form the dummy gate structure 600, a dielectric layer is formed onthe fin 404. The dielectric layer may be, for example, silicon oxide,silicon nitride, multilayers thereof, or the like, and may be depositedor thermally grown.

A gate layer is formed over the dielectric layer, and a mask layer isformed over the gate layer. The gate layer may be deposited over thedielectric layer and then planarized, such as by a CMP. The mask layermay be deposited over the gate layer. The gate layer may be formed of,for example, polysilicon, although other materials may also be used. Themask layer may be formed of, for example, silicon nitride or the like.

After the layers (e.g., the dielectric layer, the gate layer, and themask layer) are formed, the mask layer may be patterned using acceptablephotolithography and etching techniques to form the mask 606. Thepattern of the mask 606 then may be transferred to the gate layer andthe dielectric layer by an acceptable etching technique to form thedummy gate 604 and the underlying dummy gate dielectric 602,respectively. The dummy gate 604 and the dummy gate dielectric 602 covera central portion (e.g., a channel region) of the fin 404. The dummygate 604 may also have a lengthwise direction (e.g., direction B-B ofFIG. 1 ) substantially perpendicular to the lengthwise direction (e.g.,direction of A-A of FIG. 1 ) of the fin 404.

The dummy gate dielectric 602 is shown to be formed over the fin 404(e.g., over top surfaces and sidewalls of the fin 404) and over the STIregions 500 in the example of FIG. 6 . In other embodiments, the dummygate dielectric 602 may be formed by, e.g., thermal oxidization of amaterial of the fin 404, and therefore, may be formed over the fin 404but not over the STI regions 500. It should be appreciated that theseand other variations are still included within the scope of the presentdisclosure.

FIGS. 7-19 illustrate the cross-sectional views of further processing(or making) of the FinFET device 300 along cross-section A-A (along alongitudinal axis of the fin 64), as shown in FIG. 1 . In briefoverview, three dummy gate structures 600A, 600B, and 600C areillustrated over the fin 404 in the examples of FIGS. 7-11 . Forsimplicity, the dummy gate structures 600A, 600B, and 600C may sometimesbe collectively referred to as dummy gate structures 600. It should beappreciated that more or less than three dummy gate structures can beformed over the fin 404, while remaining within the scope of the presentdisclosure.

Corresponding to operation 210 of FIG. 2 , FIG. 7 is a cross-sectionalview of the FinFET device 300 including a number of lightly doped drain(LDD) regions 700 formed in the fin 404 at one of the various stages offabrication. The LDD regions 700 may be formed by a plasma dopingprocess. The plasma doping process may include forming and patterningmasks such as a photoresist to cover the regions of the FinFET device300 that are to be protected from the plasma doping process. The plasmadoping process may implant N-type or P-type impurities in the fin 404 toform the LDD regions 700. For example, P-type impurities, such as boron,may be implanted in the fin 404 to form the LDD regions 700 for a P-typedevice. In another example, N-type impurities, such as phosphorus, maybe implanted in the fin 404 to form the LDD regions 700 for an N-typedevice. In some embodiments, the LDD regions 700 abut one of the channelregions of the FinFET device 300 (e.g., the central portion of the fin404 overlaid by one of the dummy structures 600). Portions of the LDDregions 700 may extend under the dummy gate structure 600 and into thechannel region of the FinFET device 300. FIG. 7 illustrates anon-limiting example of the LDD regions 700. Other configurations,shapes, and formation methods of the LDD regions 700 are also possibleand are fully intended to be included within the scope of the presentdisclosure. For example, the LDD regions 700 may be formed after gatespacers 702/704, which will be discussed below, are formed. In someembodiments, the LDD regions 700 are omitted.

Still referring to FIG. 7 , after the LDD regions 700 are formed, insome embodiments, first gate spacers 702 are formed around (e.g., alongand contacting the sidewalls of) the dummy gate structures 600, andsecond gate spacers 704 are formed around (e.g., along and contactingthe sidewalls of) the first gate spacers 702. For example, the firstgate spacer 702 may be formed on opposing sidewalls of the dummy gatestructure 600. The second gate spacer 704 may be formed on the firstgate spacer 702. It should be understood that any number of gate spacerscan be formed around the dummy gate structures 600 while remainingwithin the scope of the present disclosure.

The first gate spacer 702 may be a low-k spacer and may be formed of asuitable dielectric material, such as silicon oxide, siliconoxycarbonitride, or the like. The second gate spacer 704 may be formedof a nitride, such as silicon nitride, silicon oxynitride, siliconcarbonitride, the like, or combinations thereof. Any suitable depositionmethod, such as thermal oxidation, chemical vapor deposition (CVD), orthe like, may be used to form the first gate spacer 702 and the secondgate spacer 704. In accordance with various embodiments, the first gatespacer 702 and the second gate spacer 704 are formed of differentmaterials to provide etching selectivity in subsequent processing. Thefirst gate spacer 702 and the second gate spacer 704 may sometimes becollectively referred to as gate spacers 702/704.

The shapes and formation methods of the gate spacers 702-704 asillustrated in FIG. 7 (and the following figures) are merelynon-limiting examples, and other shapes and formation methods arepossible. These and other variations are fully intended to be includedwithin the scope of the present disclosure.

Corresponding to operation 212 of FIG. 2 , FIG. 8 is a cross-sectionalview of the FinFET device 300 including a number of source/drain regions800 at one of the various stages of fabrication. The source/drainregions 800 are formed in recesses of the fin 404 adjacent to the dummygate structures 600. For example, the source/drain regions 800 and thedummy gate structures 600 are alternately arranged. In other words, onesource/drain region 800 is sandwiched between adjacent dummy gatestructures 600 and/or merely one side of the source/drain region 800 isdisposed next to a dummy gate structure 600. The recesses are formed by,e.g., an anisotropic etching process using the dummy gate structures 600as an etching mask, in some embodiments, although any other suitableetching process may also be used.

The source/drain regions 800 are formed by epitaxially growing asemiconductor material in the recess, using suitable methods such asmetal-organic CVD (MOCVD), molecular beam epitaxy (MBE), liquid phaseepitaxy (LPE), vapor phase epitaxy (VPE), selective epitaxial growth(SEG), the like, or a combination thereof.

As illustrated in FIG. 8 , the epitaxial source/drain regions 800 mayhave surfaces raised from respective surfaces of the fin 404 (e.g.raised above the non-recessed portions of the fin 404) and may havefacets. In some embodiments, the source/drain regions 800 of theadjacent fins may merge to form a continuous epitaxial source/drainregion (not shown). In some embodiments, the source/drain regions 800 ofthe adjacent fins may not merge together and remain separatesource/drain regions 800 (not shown). In some embodiments, when theresulting FinFET device is an n-type FinFET, the source/drain regions800 can include silicon carbide (SiC), silicon phosphorous (SiP),phosphorous-doped silicon carbon (SiCP), or the like. In someembodiments, when the resulting FinFET device is a p-type FinFET, thesource/drain regions 800 comprise SiGe, and a p-type impurity such asboron or indium.

The epitaxial source/drain regions 800 may be implanted with dopants toform source/drain regions 800 followed by an annealing process. Theimplanting process may include forming and patterning masks such as aphotoresist to cover the regions of the FinFET device 300 that are to beprotected from the implanting process. The source/drain regions 800 mayhave an impurity (e.g., dopant) concentration in a range from about1×10¹⁹ cm⁻³ to about 1×10²¹ cm⁻³. P-type impurities, such as boron orindium, may be implanted in the source/drain region 800 of a P-typetransistor. N-type impurities, such as phosphorous or arsenide, may beimplanted in the source/drain regions 800 of an N-type transistor. Insome embodiments, the epitaxial source/drain regions 800 may be in situdoped during their growth.

Corresponding to operation 214 of FIG. 2 , FIG. 9 is a cross-sectionalview of the FinFET device 300 including an interlayer dielectric (ILD)900 at one of the various stages of fabrication. In some embodiments,prior to forming the ILD 900, a contact etch stop layer (CESL) 902 isformed over the structure illustrated in FIG. 9 . The CESL 902 canfunction as an etch stop layer in a subsequent etching process, and maycomprise a suitable material such as silicon oxide, silicon nitride,silicon oxynitride, combinations thereof, or the like, and may be formedby a suitable formation method such as CVD, PVD, combinations thereof,or the like.

Next, the ILD 900 is formed over the CESL 902 and over the dummy gatestructures 600 (e.g., 600A, 600B, and 600C). In some embodiments, theILD 900 is formed of a dielectric material such as silicon oxide,phosphosilicate glass (PSG), borosilicate glass (BSG), boron-dopedphosphosilicate Glass (BPSG), undoped silicate glass (USG), or the like,and may be deposited by any suitable method, such as CVD, PECVD, orFCVD. After the ILD 900 is formed, a dielectric layer 904 is formed overthe ILD 900. The dielectric layer 904 can function as a protection layerto prevent or reduces the loss of the ILD 900 in subsequent etchingprocesses. The dielectric layer 904 may be formed of a suitablematerial, such as silicon nitride, silicon carbonitride, or the like,using a suitable method such as CVD, PECVD, or FCVD. After thedielectric layer 904 is formed, a planarization process, such as a CMPprocess, may be performed to achieve a level upper surface for thedielectric layer 904. The CMP may also remove the mask 606 and portionsof the CESL 902 disposed over the dummy gate 604. After theplanarization process, the upper surface of the dielectric layer 904 islevel with the upper surface of the dummy gate 604, in some embodiments.

An example gate-last process (sometimes referred to as replacement gateprocess) is performed subsequently to replace the dummy gate 604 and thedummy gate dielectric 602 of each of the dummy gate structures 600 withan active gate (which may also be referred to as a replacement gate or ametal gate).

Corresponding to operation 216 of FIG. 2 , FIG. 10 is a cross-sectionalview of the FinFET device 300 in which the dummy gate structures 600A,600B, and 600C (FIG. 9 ) are removed to form gate trenches 1000A, 1000B,and 1000C, respectively, at one of the various stages of fabrication.Next, upper portions of the gate trenches 1000A, 1000B, and 1000C arehorizontally expanded by removing relative upper portions of the firstgate spacers 702, such that each of the gate trenches 1000A, 1000B, and1000C has an upper trench 1000U and a lower trench 1000L, where theupper trench 1000U is wider than the lower trench 1000L horizontally.Details of forming the gate trenches 1000A-C will be discussed below.For simplicity, the gate trenches 1000A-C may sometimes be collectivelyreferred to as gate trenches 1000.

In some embodiments, to remove the dummy gate structures 600, one ormore etching steps are performed to remove the dummy gate 604 and thedummy gate dielectric 602 directly under the dummy gate 604, so that thegate trenches 1000 (which may also be referred to as recesses) areformed between respective first gate spacers 702. Each gate trench 1000exposes the channel region of the fin 404. During the dummy gateremoval, the dummy gate dielectric 602 may be used as an etch stop layerwhen the dummy gate 604 is etched. The dummy gate dielectric 602 maythen be removed after the removal of the dummy gate 604.

Next, an anisotropic etching process, such as a dry etch process, isperformed to remove upper portions of the first gate spacer 702. In someembodiments, the anisotropic etching process is performed using anetchant that is selective to (e.g., having a higher etching rate for)the material of the first gate spacer 702, such that the first gatespacer 702 is recessed (e.g., upper portions removed) withoutsubstantially attacking the second gate spacer 704 and the dielectriclayer 904. After the upper portions of the first gate spacers 702 areremoved, upper sidewalls 704SU of the second gate spacer 704 areexposed.

As illustrated in FIG. 10 , after the upper portions of the first gatespacers 702 are removed, each of the gate trenches 1000 has an uppertrench 1000U and a lower trench 1000L. The lower trench 1000L is betweenthe remaining lower portions of the first gate spacer 702. The uppertrench 1000U is over the lower trench, and is defined (e.g., bordered)by the upper sidewalls 704SU of the second gate spacer 704. FIG. 10illustrates an interface 1001 between the upper trench 1000U and thelower trench 1000L. The interface 1001 is level with an upper surface1000U of the remaining lower portions of the first gate spacer 702. Eachof the gate trenches 1000 has a wider upper trench 1000U and a narrowlower trench 1000L, which resembles the letter “Y,” and therefore, thegate trenches 1000 may sometimes be referred to as Y-shaped gatetrenches.

In some embodiments, the upper trench 1000U has a width W₁ (e.g., adistance between respective opposing upper sidewalls 704SU) betweenabout 20 nanometers (nm) and about 30 nm, and has a depth H₁ (e.g., adistance between an upper surface of the second gate spacer 704 and theinterface 1001) between about 20 nm and about 120 nm. The lower trench1000L has a width W₂ (e.g., a distance between respective opposingsidewalls of the remaining lower portions of the first gate spacer 702)between about 10 nm and about 20 nm, and has a depth H₂ (e.g., adistance between a bottom surface of the gate trench 1000 and theinterface 1001) between about 20 nm and about 40 nm. As will bedescribed in subsequent processing, metal gates (see, e.g., 1520 of FIG.15 ) are formed in the lower trenches 1000L. For example, a gateelectrode material (see, e.g., 1600 of FIG. 16 ), such as tungsten, isused to fill the lower trenches 1000L to form the gate electrode of themetal gates. Therefore, the size of the lower trench 1000L can determinethe size of the metal gates and the size of the gate electrodes.

Corresponding to operation 218 of FIG. 2 , FIG. 11 is a cross-sectionalview of the FinFET device 300 including a gate dielectric layer 1100, awork function layer 1102, an optional capping layer 1104, and a gluelayer 1106 at one of the various stages of fabrication. The gatedielectric layer 1100, the work function layer 1102, the optionalcapping layer 1104, and the glue layer 1106 are formed successively inthe gate trenches 1000.

For example, the gate dielectric layer 1100 is deposited conformally inthe gate trenches 1000, such as on the top surfaces and the sidewalls ofthe fin 404, on the top surfaces and the sidewalls of the gate spacers702/704, and on the top surface of the dielectric layer 904. Inaccordance with some embodiments, the gate dielectric layer 1100includes silicon oxide, silicon nitride, or multilayers thereof. Inexample embodiments, the gate dielectric layer 1100 includes a high-kdielectric material, and in these embodiments, the gate dielectriclayers 1100 may have a k value greater than about 7.0, and may include ametal oxide or a silicate of Hf, Al, Zr, La, Mg, Ba, Ti, Pb, andcombinations thereof. The formation methods of gate dielectric layer1100 may include molecular beam deposition (MBD), atomic layerdeposition (ALD), PECVD, and the like. A thickness of the gatedielectric layer 1100 may be between about 8 angstroms (Å) and about 20angstroms, as an example. A thickness of the gate dielectric layer 1100may be between about 5 nanometer (nm) and about 25 nm, as anotherexample.

Next, the work function layers 1102 is formed (e.g., conformally) overthe gate dielectric layer 1100. The work function layer 1102 may be aP-type work function layer, an N-type work function layer, multi-layersthereof, or combinations thereof, in some embodiments. In theillustrated example of FIG. 11 , the work function layer 1102 is anN-type work function layer. In the discussion herein, a work functionlayer may also be referred to as a work function metal. Example P-typework function metals that may be included in the gate structures forP-type devices include TiN, TaN, Ru, Mo, Al, WN, ZrSi₂, MoSi₂, TaSi₂,NiSi₂, WN, other suitable P-type work function materials, orcombinations thereof. Example N-type work function metals that may beincluded in the gate structures for N-type devices include Ti, Ag, TaAl,TaAlC, TiAlN, TaC, TaCN, TaSiN, Mn, Zr, other suitable N-type workfunction materials, or combinations thereof. A work function value isassociated with the material composition of the work function layer, andthus, the material of the work function layer is chosen to tune its workfunction value so that a target threshold voltage Vt is achieved in thedevice that is to be formed. The work function layer(s) may be depositedby CVD, physical vapor deposition (PVD), ALD, and/or other suitableprocess. A thickness of a P-type work function layer may be betweenabout 8 Å and about 15 Å, and a thickness of an N-type work functionlayer may be between about 15 Å and about 30 Å, as an example. Athickness of a P-type work function layer may be between about 5nanometer (nm) and about 25 nm, and a thickness of an N-type workfunction layer may be between about 5 nm and about 25 nm, as anotherexample.

Next, the capping layer 1104, which is optional, is formed (e.g.,conformally) over the work function layer 1102. The capping layer 1104,if formed, protects the underlying work function layer 1102 from beingoxidized. In some embodiments, the capping layer 1104 is asilicon-containing layer, such as a layer of silicon, a layer of siliconoxide, or a layer of silicon nitride formed by a suitable method such asALD, MBD, CVD, or the like. A thickness of the capping layer 1104 may bebetween about 8 Å and about 15 Å, as an example. A thickness of thecapping layer 1104 may be between about 5 nanometer (nm) and about 25nm, as another example. In some embodiments, the capping layer 1104 canbe omitted.

Next, the glue layer 1106 is formed (e.g., conformally) over the cappinglayer 1104, or over the work function layer 1102 if the capping layer1104 is omitted. The glue layer 1106 functions as an adhesion layerbetween the underlying layer (e.g., 1104) and a subsequently formed gateelectrode material over the glue layer 1106. The glue layer 1106 may beformed of a suitable material, such as titanium nitride, using asuitable deposition method such as CVD, PVD, ALD, or the like. Athickness of the glue layer 1106 may be between about 5 nanometer (nm)and about 25 nm, as an example. Depending on the width W₂ of the lowertrench 1000L and the thicknesses of the previously formed layers (e.g.,1000, 1002, 1004) in the gate trenches, the glue layer 1106 may fill theremaining portions of the lower trench 1000L, as illustrated in theexample of FIG. 11 . Further, depending on the width W₁ of the uppertrench 1000U, the width W₂ of the lower trench 1000L, and thethicknesses of the previously formed layers (e.g., 1000, 1002, 1004) inthe gate trenches, the glue layer 1106 may fill the whole trench 1000.

FIGS. 12-19 illustrate subsequent processing operations to form themetal gates of the FinFET device 300. For simplicity, FIGS. 12-19 eachillustrate only a portion of the FinFET device 300. In particular, FIG.12-19 each illustrate a zoomed-in (enlarged) view of a region 1120 inFIG. 11 . For example, FIG. 12 shows the region 1120 of FIG. 11 upon theglue layer 1109 being formed.

Corresponding to operation 220 of FIG. 2 , FIG. 13 is a cross-sectionalview of the region 1120 of the FinFET device 300 in which a portion ofthe glue layer 1106 is removed at one of the various stages offabrication. In some embodiments, the portion of the glue layer 1106 isremoved from the upper trench 1000U of the gate trench 1000 by a gluelayer pull-back process. In some embodiments, a wet etch process isperformed as the glue layer pull-back process to selectively remove theglue layer 1106 from the upper trench 1000U without attacking (e.g.,damaging, removing) the underlying layer (e.g., the capping layer 1104).The wet etch process may be end-pointed on the capping layer 1104. Thewet etch process is performed using a chemical including an acid and anoxidizer, in some embodiments. For example, the chemical used may be amixture of hydrochloric acid (HCl) and hydrogen peroxide (H₂O₂), whereHCl functions as the acid and H₂O₂ functions as the oxidizer. In someembodiments, a mixing ratio (e.g., volume ratio) between HCl and H₂O₂ isbetween about 1:1 and 1:20 for the wet etch process. The wet etchprocess may be performed at a temperature between about 40° C. and about70° C. for a duration between about 1 minute and about 5 minutes, orelse may be ended using an endpoint detection process.

As illustrated in FIG. 13 , after the glue layer pull-back process, atleast a portion of the capping layer 1104 is exposed in the upper trench1000U, and a remaining portion of the glue layer 1106 still fills thelower trench 1000L.

Corresponding to operation 222 of FIG. 2 , FIG. 14 is a cross-sectionalview of the region 1120 of the FinFET device 300 in which a portion ofthe capping layer 1104 is removed at one of the various stages offabrication. In some embodiments, the portion of the capping layer 1104is removed from the upper trench 1000U by a capping layer break-throughprocess. In some embodiments, a wet etch process is performed as thecapping layer break-through process to remove the capping layer 1104from the upper trench 1000U. In some embodiments, the wet etch processto remove the capping layer 1104 from the upper trench 1000U isperformed using a fluoride-containing chemical. For example, thefluoride-containing chemical may be a mixture of hydrofluoric acid (HF)and water (e.g., H₂O, or de-ionized water (DIW)). In some embodiments, amixing ratio (e.g., volume ratio) between HF and H₂O is between about1:100 and 1:2000 for the wet etch process. The wet etch process may beperformed at a temperature between about 20° C. and about 40° C. for aduration between about 3 minutes and about 6 minutes. As illustrated inFIG. 14 , after the capping layer break-through process, the workfunction layer 1102 is exposed in the upper trench 1000U. In someembodiments, the etching selectivity of the fluoride-containing chemicalmay not be high, and therefore, the wet etch process (the capping layerbreak-through process) is performed in a time mode. In other words, thewet etch process is timed (e.g., performed for a pre-determined periodof time) so that the capping layer 1104 in the upper trench is removedwithout substantially attacking the work function layer 1102 and/or thegate dielectric layer 1100.

As illustrated in FIG. 14 , the capping layer break-through process alsorecesses respective portions of the layers 1102, 1104, and 1106 in thelower trench 1000L. As such, the layers 1102, 1104, and 1106 in thelower trench can present a curved (e.g., concave) upper surface thatextends below the interface 1001 between the upper trench 1000U and thelower trench 1000L.

Corresponding to operation 224 of FIG. 2 , FIG. 15 is a cross-sectionalview of the region 1120 of the FinFET device 300 in which a portion ofthe work function layer 1102 is removed at one of the various stages offabrication. In some embodiments, the portion of the work function layer1102 is removed from the upper trench 1000U. In some embodiments, a wetetch process is performed to selectively remove the work function layer1102 from the upper trench 1000U without attacking the underlying gatedielectric layer 1100. The wet etch process is performed using achemical comprising a base and an oxidizer, in some embodiments. Forexample, the chemical used may be a mixture of ammonium hydroxide(NH₄OH) and hydrogen peroxide (H₂O₂), where NH₄OH functions as the baseand H₂O₂ functions as the oxidizer. In some embodiments, a mixing ratio(e.g., volume ratio) between NH₄OH and H₂O₂ is between about 1:1 and1:2001 for the wet etch process. The wet etch process may be performedat a temperature between about 40° C. and about 70° C. for a durationbetween about 1 minute and about 5 minutes, or else may be ended usingan endpoint detection process.

As illustrated in FIG. 15 , after the wet etch process, a first portion1100A of the gate dielectric layer 1100 is exposed in the upper trench1000U, and a second portion 1100B of the gate dielectric layer 1100 isoverlaid by (or in contact with) the layers 1102, 1104, and 1106 in thelower trench 1000L. FIG. 15 also illustrates a height H₃ measuredbetween a lowest position (e.g., closest to the substrate 302) of thecurved upper surface of the layers 1102, 1104, and 1106 in the lowertrench and the interface 1001 between the upper trench 1000U and thelower trench 1000L. In some embodiments, H₃ is between about 3 nm andabout 12 nm. In some embodiments, the remaining portions of the variouslayers in the lower trench 1000L, such as the work function layer 1102,the capping layer 1104, and the glue layer 1106 can at least partiallyform a metal gate 1520. Accordingly, the upper surface of the metal gate1520 may extends below the upper surface of the first gate spacer 702 byH₃.

Corresponding to operation 226 of FIG. 2 , FIG. 16 is a cross-sectionalview of the region 1120 of the FinFET device 300 in which a metalstructure 1600 is formed at one of the various stages of fabrication.The metal structure 1600 may include a suitable metal, such as tungsten(W), formed by a suitable method, such as PVD, CVD, electroplating,electroless plating, or the like. Besides tungsten, other suitablematerial, such as copper (Cu), gold (Au), cobalt (Co), combinationsthereof, multi-layers thereof, alloys thereof, or the like, may also beused as the metal structure 1600.

As illustrated in FIG. 16 , a metal material (e.g., tungsten) isdeposited in the trench 1000 to be in contact with the curved uppersurface of the layers 1102, 1104, and 1106 (or of the layer 1106 only)in the lower trench 1000L so as to form the metal structure 1600. Inaccordance with various embodiments, by overlaying the gate spacers702/704 with a portion of the gate dielectric layer 1100 (e.g., thefirst portion 1100A), which includes one or more high-k dielectricmaterials, it can avoid the gate spacers 702/704 from being attachedwith the metal material while forming the metal structure 1600. Such anattachment of the metal material is generally referred to as “selectiveloss.” Even though a relatively small amount of the selective lossexists along the gate dielectric layer 1100 in the upper trench 1000U,such a portion of the gate dielectric layer 1100 can be effectivelyremoved by using a wet etching solution that selectively removes amaterial of the gate dielectric layer 1100 while remaining the metalstructure 1600 (and the underlying layers 1102-1104) substantiallyintact. The wet etching solution will be discussed in further detailbelow. Moreover, as the respective top surfaces of the spacers 702 areoverlaid by the gate dielectric layer 1100 while forming the metalstructure 1600, the metal material, which could have been formed on thetop surfaces of the spacers 702 (typically knows as “antennas”), canalso be minimized. Such antennas can deteriorate the insulationcharacteristic of a dielectric material to be filled in the gate trench.The dielectric material is typically used to electrically insulate agate contact from adjacent gate contacts. By minimizing the amount ofundesired metal material of the metal structure to be attached to thegate spacers 702/704, when the gate trench 1000 is later filled withsuch a dielectric material, an insulation characteristic of thedielectric material will not be compromised, thereby improvingperformance (e.g., reducing leakage current) of the FinFET device 300 asa whole.

Corresponding to operation 228 of FIG. 2 , FIG. 17 is a cross-sectionalview of the region 1120 of the FinFET device 300 in which the portion ofthe gate dielectric layer 1100 (e.g., 1100A shown in FIG. 16 ) in theupper trench 1000U is removed at one of the various stages offabrication. The portion of the gate dielectric layer 1100 may beremoved by a wet etch process using a wet etching solution 1700(indicated by Xs in FIG. 17 ). In an embodiment, the wet etchingsolution 1700 selectively removes the material of the gate dielectriclayer 1100 at a faster rate than the material of the metal structure1600, thereby allowing the wet etching solution 1700 to effectivelyremove the gate dielectric layer 1100 in the upper trench 1000U. Assuch, while the precise components of the wet etching solution 1700 willbe dependent at least in part on the materials chosen for the metalstructure 1600 and the gate dielectric layer 1100, in an embodiment inwhich the metal structure 1600 includes tungsten and the gate dielectriclayer 1100 includes one or more high-k dielectric materials, the wetetching solution 1700 may include an etchant and an oxidant placed intoa solvent. It should be appreciated that the wet etching solution 1700and corresponding processing conditions, which will be discussed below,may be used on the metal structure 1600 and the gate dielectric layer1100 that include materials other than the tungsten and the high-kdielectric material, respectively, while remaining within the scope ofthe present disclosure.

For example, the etchant may be an amine with a formula such as R—NH₂,R—N—R′, NR₁R₂R₃, combinations of these, or the like, wherein each of R,R′, R₁, R₂ and R₃ may be an alkyl group, a phenyl group, or the like. Inother embodiments the etchant may be an amine such astetramethylammonium hydroxide (TMAH), ammonium hydroxide (NH₄OH),tetrabutylammonium hydroxide (TBAH), combinations of these, or the like.However, any suitable etchant may be utilized.

The oxidant may be used in conjunction with the etchant in order to helpcontrol the corrosion potential between the materials of the metalstructure 1600 and the gate dielectric layer 1100. In the above examplewhere the metal structure 1600 includes tungsten and the gate dielectriclayer 1100 includes one or more high-k dielectric materials, the oxidantmay be a fluoride-based acid, for example, hydrofluoric acid (HF),fluoroantimonic acid (H₂FSbF₆), etc. In some embodiments, the oxidantmay be a mixture of the fluoride-based acid with one or more other acidssuch as, for example, perchloric acid (HClO₄), chloric acid (HClO₃),hypochlorous acid (HClO), chlorous acid (HClO₂), metaperiodic acid(HClO₄), iodic acid (HIO₃), iodous acid (HIO₂), hypoiodous acid (HIO),perbromic acid (HBrO₄), bromic acid (HBrO₃), bromous acid (HBrO₂),hypobromous acid (HBrO), nitric acid (HNO₃), combinations of these, orthe like. However, any suitable oxidant may be utilized.

Optionally, if desired, a stabilizer may be added along with the oxidantin order to stabilize the oxidant. In an embodiment the stabilizer maybe a chelator such as ethylenediaminetetraacetic acid (EDTA),1,2-cyclohexanedinitrilotetraacetic acid (CDTA), histidine,diethylenetriamine pentaacetic acid (DTPA), combinations of these, orthe like. However, any suitable stabilizer may be utilized.

In an embodiment, the etchant, oxidizer, and stabilizer are all placedwithin a solvent in order to mix, handle, and eventually deliver the wetetching solution 1700. In an embodiment, the solvent may be an organicsolvent such as ethylene glycol (EG), diethylene glycol (DEG),1-(2-hydroxyethyl)-2-pyrrolidinone(HEP), dimethyl sulfoxide (DMSO),sulfolane, combinations of these, or the like. However, any suitablesolvent may be utilized.

In particular embodiments the etchant may be placed within the solventto a concentration of between about 0.5%-volume and about 15%-volume,such as about 2%-volume. Additionally, the oxidant may be placed intothe solvent to a concentration of between about 3%-volume and about20%-volume, and the stabilizer may be added to a concentration ofbetween about 0.1%-volume and about 5%-volume, such as about 1%-volume.The solvent can make up a remainder of the wet etching solution 1700and, as such, may have a concentration of between about 5%-volume andabout 90%-volume, such as about 60%-volume. However, any suitableconcentrations may be utilized.

By utilizing the etchants, oxidants, stabilizers, and solvent describedherein, the selectivity of the wet etching solution to the material ofthe gate dielectric layer 1100 (e.g., the high-k materials) to the metalstructure 1600 (e.g., tungsten) can be tuned. In some embodiments, sucha selectivity for the wet etching solution 1700 can be chosen betweenabout 4 and about 9, such as about 5. However, any suitable selectivitycan be utilized.

The wet etching solution 1700 is placed in contact with both the gatedielectric layer 1100 in the upper trench 1000U (e.g., 1100A shown inFIG. 16 ) and the metal structure 1600. In an embodiment, the wetetching solution 1700 may be placed using a dip method, a spray onmethod, a puddle method, combinations of these, or the like. During theetching process, the wet etching solution 1700 may be kept at atemperature of between about 25° C. and about 70° C., such as about 50°C., for a time of between about 1 min and about 10 min, such as about 4min. However, any suitable process conditions may be utilized.

At the end of the etching process (e.g., at the end of the timed etch),the wet etching solution 1700 is removed and the portion of the gatedielectric layer 1100 has been removed down to the lower trench 1000L.However, because the wet etching solution 1700 is much more selective tothe material of the gate dielectric layer 1100, the material of themetal structure 1600 remains substantially intact. As such, the metalstructure 1600 remains to extend from the lower trench 1000L to bewithin the upper trench 1000U. The metal structure 1600 can have aheight, H₄, which is between the height of the gate spacers 702 and theheight of the gate spacers 704. For example, H₄ may range between about5 nm and about 25 nm, such as about 10 nm. Similarly, the metalstructure 1600 can have a width, W3, which ranges between about 2 nm andabout 10 nm, such as about 4 nm. However, any suitable dimensions may beutilized.

By selectively etching the gate dielectric layer 1100 over the metalstructure 1600, the metal structure 1600 remains at the end of the wetetching process. As such, there is less of a chance that the underlyinglayers (e.g., layers 1102, 1104, and 1106) will be exposed to the wetetching solution 1700, thereby less chance of damage to these underlyinglayers, which constitute at least a portion of a metal gate. With lesspotential for damage, there is less chance for defects, therebyincreasing the reliability of the process. Further, in some embodiments,the etchants, oxidants, stabilizers, and solvent and the parameters forthe etching process, as described herein, may be selected to cause thewet etching solution 1700 to selectively etch the gate dielectric layer1100 over not only the metal structure 1600 but also the layers 1102,1104, and 1106.

In some embodiments, the metal structure 1600 forms a gate electrode1600. As illustrated in FIG. 17 , the gate electrode 1600 contacts(e.g., physically contacts) the metal gate 1520. Specifically, in themetal gate 1520, the (remaining) work function layer 1102, and the(remaining) capping layer 1104 each have a U-shaped cross-section. Theglue layer 1106 is vertically disposed between the gate electrode 1600and the capping layer 1104; and horizontally disposed between twoopposing inner sidewalls of the U-shaped work function layer 1102, andbetween two opposing inner sidewalls of the U-shaped gate dielectriclayer 1100. The wet etch process etches the second portion 1100B of thegate dielectric layer 1100 with the gate electrode 1600 exposed in thewet etching solution 1700, to leave the gate electrode 1600substantially intact.

Corresponding to operation 228 of FIG. 2 , FIG. 18 is a cross-sectionalview of the region 1120 of the FinFET device 300 including a dielectricmaterial 1800 at one of the various stages of fabrication. Thedielectric material 1800 (e.g., silicon oxide, silicon nitride, a low-kdielectric material, or the like) is formed in the gate trench 1000,using a suitable formation method such as PVD, CVD, or the like. In someother embodiments, the gate trench 1000 may be first filled with asemiconductor material, such as silicon, and after a gate contact (e.g.,1900 in FIG. 19 ) is formed, the semiconductor material is replaced withthe dielectric material 1800. For example, after a gate contact isformed, the semiconductor material may be removed by an etching processusing an etchant that is selective to the semiconductor material. Afterthe semiconductor material is removed, the dielectric material 1800 isformed to fill the space previously occupied by the semiconductormaterial.

Corresponding to operation 230 of FIG. 2 , FIG. 19 is a cross-sectionalview of the region 1120 of the FinFET device 300 including a gatecontact 1900 at one of the various stages of fabrication. The gatecontact 1900 is formed in (e.g., to extend through) the dielectricmaterial 1800 to electrically couple to the gate electrode 1600. In theabove example where the dielectric material 1800 is deposited prior toforming the gate contact 1900 (also referred to as contact plugs), acontact opening is formed in the dielectric material 1800 to expose thegate electrode 1600, using, e.g., photolithography and etching. Once thecontact opening is formed, a barrier layer 1902, a seed layer 1904, anda fill metal 1906 are formed successively in the contact opening to formthe gate contact 1900.

The barrier layer 1902 includes an electrically conductive material suchas titanium nitride, although other materials, such as tantalum nitride,titanium, tantalum, or the like, may alternatively be utilized. Thebarrier layer 1902 may be formed using a CVD process, such as PECVD.However, other alternative processes, such as sputtering, metal organicchemical vapor deposition (MOCVD), or ALD, may alternatively be used.

The seed layer 1904 is formed over the barrier layer 1902. The seedlayer 1904 may include copper, titanium, tantalum, titanium nitride,tantalum nitride, the like, or a combination thereof, and may bedeposited by ALD, sputtering, PVD, or the like. In some embodiments, theseed layer 1904 is a metal layer, which may be a single layer or acomposite layer comprising a plurality of sub-layers formed of differentmaterials. For example, the seed layer 1904 may include a titanium layerand a copper layer over the titanium layer.

The fill metal 1906 is deposited over the seed layer 1904, and fills theremaining portions of the contact opening. The fill metal 1906 may be ametal-containing material such as copper (Cu), aluminum (Al), tungsten(W), the like, combinations thereof, or multi-layers thereof, and may beformed by, e.g., electroplating, electroless plating, or other suitablemethod. After the formation of the fill metal 1906, a planarizationprocess, such as a CMP, may be performed to remove the excess portionsof the barrier layer 1902, the seed layer 1904, and the fill metal 1906,which excess portions are over the upper surface of the dielectric layer904 (referring again to FIG. 11 ) and over the upper surface of thesecond gate spacer 704. The resulting remaining portions of the barrierlayer 1902, the seed layer 1904, and the fill metal 1906 thus form thegate contact 1900.

FIG. 20 shows the cross-sectional view of the FinFET device 300 afterthe gate contact(s) 1900, electrically coupling to the respective metalgates 1702, are formed. As shown, metal gates 1520A, 1520B, and 1520C,which replaced respective portions of the dummy gate structure 600A,600B, and 600C (FIG. 9 ), respectively, are formed over the fin 404. Themetal gates 1520A-C may sometimes be collectively referred to as “metalgates 1520.” It should be appreciated that additional processing may beperformed to finish the fabrication of the FinFET device 300, such asforming source/drain contacts and forming metallization layers over thedielectric layer 904. For brevity, details with respect to thosestructures are not discussed herein.

As semiconductor manufacturing process continues to advance, thedistance (e.g., pitch) between adjacent metal gates 1520 are gettingcloser and closer. For advanced processing nodes such as 5 nm or beyond,the small pitch between metal gates 1520 may cause metal gate leakage,which decreases the reliability of the device formed. By protecting thegate spacers 702/704 with the gate dielectric layer 1100 while formingthe gate electrode 1600, the amount of undesired metal material (of thegate electrode 1600) to be attached to the gate spacers 702/704 can bereduced or eliminated. Accordingly, deterioration or damage to theinsulation characteristic of the dielectric material 1800 can beminimized, thereby helping to increase the reliability of the deviceformed.

In the example of FIG. 20 , the illustrated metal gates 1520 have a samestructure (e.g., same film scheme in the metal gates). In otherembodiments, the metal gates 1520 may have respective differentstructures. For example, each of the metal gates 1520 may have differentwork function layer(s) to achieve different threshold voltages, and/orto form metal gates in different regions (e.g. N-type device region orP-type device region) of the FinFET device 300. An example isillustrated in FIG. 21 .

Referring to FIG. 21 , a cross-sectional view of portions of a FinFETdevice 300A is shown. The FinFET device 300A is substantially similar tothe FinFET device 300 shown in FIG. 20 , but with different workfunction layer(s) for each metal gate. For simplicity, FIG. 21 onlyillustrates portions of the FinFET device 300A adjacent to the metalgates 1520A, 1520B, and 1520C. The metal gates 1520A, 1520B, and 1520Care separated by dividers 2101, where the dividers 2101 includeadditional features (see, e.g., FIG. 20 ) between the metal gates 1520A,1520B, and 1520C that are omitted for simplicity.

As shown, the metal gate 1520A is the same as the metal gate 1520A inFIG. 20 , which includes an N-type work function layer 1102. The metalgate 1520B of FIG. 21 , however, includes two work function layers. Forexample, the metal gate 1520B includes a P-type work function layer 2100contacting (e.g., physically contacting) and extending along the gatedielectric layer 1100, and includes the same N-type work function layer1102 contacting (e.g., physically contacting) and extending along theP-type work function layer 2100 and a portion of the gate dielectriclayer 1100. Note that while the N-type work function layer 1102 of themetal gate 1520A has a U-shaped cross-section, the N-type work functionlayer 1102 of the metal gate 1520B has laterally extended portionconnected to the ends of the U-shaped cross-section, respectively, whichmay due to the dual-work function layer structure of the metal gate1520B having less space available for the N-type work function layer1102. The metal gate 1520C of FIG. 21 is similar to the metal gate 1520Bof FIG. 20 , but with a different P-type work function layer 2102.

The present disclosure provides many advantages for forming FinFETdevices having the metal gates 1520 with different film schemes (e.g.,different work function layers). Here the term film scheme refers to thematerials and the structure of the stack of layers (e.g., 1100, 1102,1102 and 2100, 1102 and 2102, 1104, and 1106) of the metal gates 1520.Due to the different film schemes (e.g., different work function layers)of the metal gates in the gate trenches 1000A-C, the etch rates for thedifferent combinations of layers in the gate trenches are different,which results in a loading effect (e.g., non-uniformity) in the removalof the layers in the gate trenches. In other words, the amount ofremoved layers in the gate trenches are different. This may result inthe gate heights of the subsequently formed metal gates 1520A-C to benon-uniform. As such, the different film schemes of the different metalgates 1520A-C may have different heights. The presently disclosed methodhelps to protect the underlying structures by forming the gate electrode1600 over the metal gates 1520 prior to selectively etching the portionof the gate dielectric layer 1100 not overlaid by the gate electrode1600. In this way, more of the material of the gate electrode 1600remains intact during the selective etching process, helping to preventunintended over-etches that damage the underlying layers. As such,damage to the metal gates 1520 is avoided and the critical dimension ofthe metal gates 1520 can be preserved.

Referring to FIG. 22 , a cross-sectional view of portions of a FinFETdevice 300B is shown. The FinFET device 300B is substantially similar tothe FinFET device 300 shown in FIG. 20 , but with an additional metalgate 1520D. For simplicity, FIG. 22 only illustrates portions of theFinFET device 300B adjacent to the metal gates 1520A and 1520D. Themetal gates 1520A and 1520D are separated by a divider 2201, where thedivider 2201 includes additional features (see, e.g., FIG. 20 ) such as,the metal gate 1520B and 1520C that are omitted for simplicity.

As shown, the metal gate 1520A is the same as the metal gate 1520A inFIG. 20 , which, together with a corresponding gate dielectric layer1100, extend over a distance that defines a channel length, L₁, of acorresponding transistor. The metal gate 1520D, together with acorresponding gate dielectric layer 1100, however, extend over adistance that defines a channel length, L₂, which is substantiallygreater than L₁. Such a transistor with the relatively short channellength (e.g., the transistor having the metal gate 1520A) may sometimesbe referred to as a short-channel transistor; and such a transistor withthe relatively long channel length (e.g., the transistor having themetal gate 1520D) may sometimes be referred to as a long-channeltransistor. In the example of the long-channel transistor, the metalgate 1520D may further include a metal fill 2200 (e.g., tungsten) and adielectric fill 2202 (e.g., silicon oxide, silicon nitride, a low-kdielectric material, or the like). Partially due to the relatively longchannel length, each of the layers 1100, 1102, 1104, and 1106 of themetal gate 1520D may have a U-shaped cross-section, and the metal fill2200, which may also have a U-shaped cross-section, contacts (e.g.,physically contacts) the glue layer 1106. Further, the metal gate 1520Dcan include an additional gate electrode 1600. Each of the gateelectrodes 1600 electrically couples to one of the ends of a combinationof the U-shaped layers 1102, 1104, and 1106 and the U-shaped metal fill2200. Accordingly, one or more gate contacts 1900 may be formed tocouple the gate electrodes 1600.

In one aspect of the present disclosure, a method of manufacturing asemiconductor device is disclosed. The method includes forming a gatetrench over a semiconductor fin. The gate trench includes an upperportion surrounded by first gate spacers and a lower portion surroundedby second gate spacers and the first gate spacers. The method includesforming a metal gate in the lower portion of the gate trench. The metalgate is disposed over a first portion of a gate dielectric layer. Themethod includes depositing a metal material in the gate trench to form agate electrode overlaying the metal gate in the lower portion of thegate trench, while keeping sidewalls of the first gate spacers and uppersurfaces of the second gate spacer overlaid by a second portion of thegate dielectric layer. The method includes removing the second portionof the gate dielectric layer, while remaining the gate electrodesubstantially intact.

In another aspect of the present disclosure, a method of manufacturing asemiconductor device is disclosed. The method includes removing a dummygate structure that overlays a portion of a semiconductor fin. Themethod includes forming a metal gate over the portion of thesemiconductor fin, the metal gate including a first portion of a gatedielectric layer. The method includes depositing a metal material toform a gate electrode contacting the metal gate, while exposing a secondportion of the gate dielectric layer. The method includes etching thesecond portion of the gate dielectric layer with the gate electrodeexposed during the etching. The gate electrode remains substantiallyintact.

In yet another aspect of the present disclosure, a semiconductor deviceis disclosed. The semiconductor device includes a semiconductor fin. Thesemiconductor device includes first spacers over the semiconductor fin.The semiconductor device includes second spacers over the semiconductorfin, the second spacers extending farther from the semiconductor finthan the first spacers. The semiconductor device includes a metal gate,over the semiconductor fin, that is sandwiched by the first spacers,which are further sandwiched by the second spacers. The semiconductordevice includes a gate electrode contacting an upper surface of themetal gate, wherein the gate electrode does not extend over the firstspacers or the second spacers.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor fin; a metal gate disposed over the semiconductor fin; agate dielectric layer disposed between the semiconductor fin and themetal gate; spacers sandwiching the metal gate; and a gate electrodecontacting the metal gate and the gate dielectric layer at a firstinterface and a second interface, respectively, wherein the firstinterface is below the second interface, and wherein a top surface ofthe gate electrode is above a top surface of the gate dielectric layer.2. The semiconductor device of claim 1, wherein the metal gate furthercomprises: a work function layer; a capping layer; and a glue layer. 3.The semiconductor device of claim 2, wherein the gate electrode contactsa top surface of each of the work function layer, the capping layer, andthe glue layer.
 4. The semiconductor device of claim 1, wherein thefirst interface and the second interface are connected to form a curvedinterface.
 5. The semiconductor device of claim 1, wherein the spacersinclude a first spacer contacting the gate dielectric layer and a secondspacer contacting the first spacer, the first spacer and the secondspacer having different heights.
 6. The semiconductor device of claim 5,wherein a top surface of the first spacer is below the top surface ofthe gate electrode, and wherein a top surface of the second spacer isabove the top surface of the gate electrode.
 7. The semiconductor deviceof claim 1, further comprising a dielectric layer disposed over the gateelectrode, wherein a bottom surface of the gate electrode is below abottom surface of the dielectric layer.
 8. The semiconductor device ofclaim 7, wherein a first portion of the spacers contacts the bottomsurface of the dielectric layer, and wherein a second portion of thespacers contacts a sidewall surface of the dielectric layer.
 9. Asemiconductor device, comprising: a semiconductor fin; a metal gatedisposed over the semiconductor fin; a gate dielectric layer disposed onsidewalls of the metal gate; a gate electrode contacting the metal gateand the gate dielectric layer along a curved surface, wherein a topsurface of the gate electrode is above a top surface of the gatedielectric layer; and a dielectric layer disposed over the gateelectrode, wherein a top portion of the gate electrode is embedded inthe dielectric layer.
 10. The semiconductor device of claim 9, furthercomprising a contact plug disposed in the dielectric layer, the contactplug contacting the top surface of the gate electrode.
 11. Thesemiconductor device of claim 9, wherein a bottom surface of the gateelectrode is below the top surface of the gate dielectric layer.
 12. Thesemiconductor device of claim 9, further comprising a first spacercontacting the gate dielectric layer and a second spacer contacting thefirst spacer, wherein the top surface of the gate electrode is between atop surface of the first spacer and a top surface of the second spaceralong a vertical direction.
 13. The semiconductor device of claim 12,wherein a sidewall of the dielectric layer contacts the second spacerbut not the first spacer.
 14. The semiconductor device of claim 12,wherein a sidewall of the gate electrode is separated from the secondspacer by a portion of the dielectric layer along a lateral direction.15. The semiconductor device of claim 9, wherein the curved surface is afirst curved surface, and wherein a sidewall of the gate electrodecontacts the dielectric layer along a second curved surface.
 16. Asemiconductor device, comprising: a semiconductor fin; a metal gatedisposed over the semiconductor fin; a gate dielectric layer disposed onsidewalls of the metal gate; a gate electrode contacting the metal gateand the gate dielectric layer along a curved surface, wherein a topsurface of the gate electrode is above a top surface of the gatedielectric layer; and a dielectric layer disposed over the gateelectrode, wherein the top surface of the gate electrode is above abottom surface of the dielectric layer.
 17. The semiconductor device ofclaim 16, wherein the metal gate includes a work function layer and aglue layer, the glue layer extending between sidewall portions of thework function layer.
 18. The semiconductor device of claim 17, whereinthe metal gate further includes a capping layer disposed between thework function layer and the glue layer.
 19. The semiconductor device ofclaim 18, further comprising a first spacer contacting the gatedielectric layer and a second spacer contacting the first spacer, thefirst spacer and the second spacer having different heights.
 20. Thesemiconductor device of claim 16, further comprising a contact plugdisposed in the dielectric layer, the contact plug contacting the topsurface of the gate electrode.